The present invention relates to a composition having lubricity and a product comprising the composition (hereinafter referred to as slide product). Particularly, the present invention relates to a composition having lubricity such as a lubricating resinous composition, lubricating elastomer composition, and a lubricating coating film composition capable of continuously oozing a lubricant to a slide interface little by little; an additive imparting lubricity to a base material; and a slide product using these compositions. Representative slide products are a slide bearing, a retainer for a holding a roll of a rolling bearing, and a seismically isolated apparatus.
Among demands growing year by year for the composition having lubricity such as a resinous slide member obtained by molding the lubricating resinous composition, a material having rubber elasticity, and a lubricating coating film, the strong demands are that they have low degree of friction and wear in an initial time and they maintain their initial sliding property for a long time. For low degree of friction and wear, a solid lubricant such as graphite, polytetrafluoroethylene (hereinafter referred to as PTFE), molybdenum disulfide (MoS2), boron nitride (BN) or the like is added to resin or a reinforcing material such as glass fiber and carbon fiber is added thereto to impart slide characteristic to the composition having lubricity. However, only the addition of the solid lubricant has a limitation in lowering the friction characteristic. Under these circumstances, a method of adding lubricating oil or the like has been carried out.
As the additive imparting lubricity to a base material, solid lubricants such as graphite, PTFE, molybdenum disulfide, boron nitride and the like are known. Base materials improve lubricity by adding the solid lubricants to the base materials such as resin, rubber, and the coating film. However, only the addition of the solid lubricant has a limitation in lowering a coefficient of friction and is incapable of allowing materials to have lower degree of friction. For achieving lower degree of friction, boundary lubrication by means of oil is generally adopted. For example, if a state in which the lubricating oil is always present on a slide interface can be maintained by adding the lubricating oil to a material, the material is allowed to have a lower degree of friction.
But the addition of only the lubricant to the resinous material or the like causes the following problems: In the case where only the lubricating oil is dispersed in the resinous material as the lubricant, the dispersion unit of the oil changes owing to kneading. Thus it is difficult to reliably manufacture a material having uniform slide characteristic.
To improve the slide characteristic of the resinous material such as the friction characteristic thereof, it is preferable that the addition amount of the lubricating oil is large. However, if the addition amount of the lubricating oil is large, a screw slip in a kneading time and metering time period is not uniform, which causes a cycle time to be long. Thus stable manufacturing is difficult. In addition, oil attaches to a die and a size accuracy is unstable. Further, if the lubricating oil and the base material are not compatible with each other, the lubricating oil cannot be dispersed into the base material, depending on the combination thereof.
In the lubricating oil-containing resinous material, a resinous layer of the base is worn little by little at a slide time and a lubricating oil layer appears on the slide portion. That is, the lubricating oil oozes on the surface of the slide portion. It is difficult to control the oozing condition of the lubricating oil. Thus there is a possibility that a pore from which the lubricating oil has oozed causes reduction of strength of the resinous layer.
In the case where a filler is added to the base material to improve the mechanical strength and wear resistance of the composition having lubricity, oil is locally present on the interface of the filler. Thus a sufficient reinforcing effect cannot be obtained.
The slide product obtained by molding the composition includes a slide bearing, a retainer for a rolling bearing, a seismically isolated apparatus, and the like.
The conventional retainer for a rolling bearing is made from metal, polyamide resin, polyacetal resin, polybutylene terephthalate resin, and the like. In molding synthetic resin, injection-moldable synthetic resin or a synthetic resinous composition reinforced with glass fiber, carbon fiber or organic fiber added to a molding material of the synthetic resin has been used. Semi-solid lubricant such as lubricating oil or grease has been used to lubricate the retainer-incorporated rolling bearing.
In the case where the semi-solid lubricant such as grease is used, resistance to stirring is generated by the consistency of the lubricant. Therefore, when a rotary shaft supported by the bearing rotates, a required torque is applied and a torque fluctuation is generated. In the conventional bearing incorporating the retainer owing to grease lubrication, when the rotational speed of the inner ring or the outer ring is as high as about 10,000 rpm, the resistance to stirring generated by the consistency of the grease causes a required torque for rotating the rotary shaft supported by the bearing to be high and a torque fluctuation to occur. Further, owing to the presence of the grease, a comparatively large amount of dust floats in the periphery of the bearing. Owing to such an increase and fluctuation of torque, generation of dust, and generation of noise caused by the rotation of the bearing, there is reduction of the performance of a bearing, especially a bearing having a diameter not more than 6 mm, which is incorporated in office appliances such as an HDD, a VTR, a DAT, a LBP and audio appliances, peripheral appliances, and the like.
To improve these problems, there are proposed a retainer, for a rolling bearing, composed of a material having a lubricating function. In Japanese Patent Application Laid-Open No.61-6429, there is disclosed the bearing containing polyamide-imide resin porously compression-molded and impregnated with fluorinated oil. According to Japanese Patent Application Laid-Open No.1-93623, the retainer formed by molding oil-containing plastic consisting of the oil-containing binder and the matrix is impregnated with lubricating oil. According to Japanese Patent Application Laid-Open No.8-21450, the mixture of polyolefin resin and the lubricating oil is molded into the configuration of the retainer. According to Japanese Patent Application Laid-Open No.2000-97241, the mixture of synthetic resin and the inorganic porous particulate matter is molded into the configuration of the retainer.
However, the retainer disclosed in Japanese Patent Application Laid-Open No.61-6429 is inferior to a retainer composed of a precise porous material in its mechanical strength. Thus depending on a use condition, the retainer lacks strength. Further because interconnected pores are formed, powdery resin is compression-molded, sintered, and then machined. Thus a large number of manufacturing processes are required.
In the case of the retainer disclosed in Japanese Patent Application Laid-Open No.1-93623, to increase oil absorption capacity, it is necessary to immerse the retainer in the lubricating oil at a high temperature (120xc2x0 C.-130xc2x0 C.) for a long time (about seven days). Therefore, there is a possibility that the lubricating oil and the resin forming the retainer deteriorate and dimensions change greatly. That is, the method is inferior in the stability of products. Another disadvantage is that the lubricating oil oozes at a comparatively early time. Thus the retainer is incapable of maintaining stable lubricity for a long time.
In the case of the retainer disclosed in Japanese Patent Application Laid-Open No.8-21450, the lubricating oil is held by polyolefin resin because the polyolefin resin is highly absorbent of oil. Thus little oil oozes from the retainer. Even though the lubricating oil is uniformly dispersed in the polyolefin resin, the lubricating oil in the vicinity of the surface of the retainer oozes. However, it is technically difficult to ooze the lubricating oil from the inside of the retainer at a stable speed for a long time.
Another problem is that if much lubricating oil is added to the polyolefin resin, problems occur in the production of the retainer. For example, it is likely that a screw slip in a kneading time, metering is unstable, which causes a cycle time to be long, a size accuracy is unstable, and the lubricating oil attaches to the surface of a die, which causes the finish of a molded product to be poor.
In the case of the retainer disclosed in Japanese Patent Application Laid-Open No.2000-97241, the lubricating oil is not held inside the resin and when oil supply is stopped, the lubricating oil is supplied to a slide interface owing to capillary action. Thus the lubricating oil does not ooze at a uniform speed from the inside for a long time.
A seismically isolated apparatus supports a multistory structure such as buildings and towers; a low structure such as single-family houses; a public structure such as bridges over roads and for railways, and the like and reduces the degree of a seism-caused force applied thereto. That is, escape from a seism means reduction of the degree of a seism-caused force applied to buildings or the like by using a method. Widely used is a seismically isolated apparatus or a seismically isolating method of base insulation type of reducing the degree of a seism-caused force applied to a building by inserting an apparatus between the base or footing and the building.
For example, a seismically isolated apparatus constructed of a combination of a slide support and a horizontal spring is hitherto used.
The seismically isolated apparatus is so constructed as to slide two plates on each other. One of the two plates is installed on a slide material such as a resinous slide plate bonded to a footing of the slide support. The other metal plate is installed on a pillar. That is, by sliding the building according to a seism-caused horizontal shaking of the ground, a force greater than a frictional force acting on a slide surface is applied to the building. The horizontal spring restricts the movable range of the building to prevent the location of the building from moving much. The lower the friction coefficient of the support material is, the higher seism escape effect is. Thus to display the seism escape effect securely, the support material is required to have a stable low friction coefficient.
Therefore, a fluorine-containing material such as PTFE resin having a low coefficient of friction is frequently used for the slide material.
However, although the PTFE resin has a low friction coefficient, it is inferior in wear resistance and compression characteristic. Thus the PTFE resin is used as a composite material containing a filler such as glass fiber. A favorable escape from a seism is realized by using the PTFE resin for the slide surface. But in designing a seismically isolated apparatus capable of withstanding a big seism and suitable for a large building, it is necessary to consider the increase of the slide speed. Therefore, the conventional material cannot comply with such a requirement. In a slide friction, the friction coefficient increases with the increase of the slide speed. Thus to allow the seismically isolated apparatus to display excellent effect of escape from a big seism, it is necessary to reduce the friction coefficient of the slide surface and reduce the dependency of the friction coefficient on the slide speed.
The larger the building is, the higher the surface pressure is. The PTFE resin is a soft resin. Thus even though resistance to creep is improved by adding a filler, there is a limit in a load-applying capability. Thus under a high load-applied state, a compression deformation amount increases with elapse of time and the contact area on the slide surface increases. Consequently, the friction coefficient increases. The increase of the slide speed and the surface pressure leads to the increase of wear.
It is an object of the present invention to provide a composition having lubricity capable of supplying a lubricant continuously to the surface of a slide surface and having a low degree of friction and wear, and an additive imparting lubricity to a base material.
It is another object of the present invention to provide a slide bearing formed by molding the composition.
It is still another object of the present invention to provide a retainer for a rolling bearing formed by molding the composition. The retainer for the rolling bearing stabilizes the rotational torque of the rolling bearing at a low value, prevents generation of dust and noise, has preferable mechanical characteristic, and is durable.
It is still another object of the present invention to provide a seismically isolated apparatus reducing the friction coefficient of a material composing a slide surface, having an improved wear resistance thereof, and improved resistance to load.
The composition having lubricity of the present invention comprises a base material, a porous silica, and a lubricant. The porous silica is impregnated with the lubricant. The porous silica has interconnected pores and is spherical and porous. The spherical porous silica is a true spherical silica particle which comprises an aggregation of primary silica particles whose average diameter is in the range of 3-8 nm. The average diameter of said true spherical silica particle is in the range of 0.5-100 xcexcm.
The other spherical porous silica is a precipitated silica particle that is an aggregation of primary particles whose diameters are not less than 15 nm.
The base material is synthetic resin, a material having rubber elasticity or a material that can be formed as a coating film. The lubricant is at least one lubricating substance selected from the group consisting essentially of lubricating oil, wax, and a greasy substance.
An additive imparting lubricity to a base material comprises porous silica and a lubricant to be impregnated into the porous silica.
The present inventor has found that in adding the lubricant to the base material to obtain a slide material having durable slide characteristic, it is possible to improve the friction and wear characteristics thereof and maintain the friction and wear characteristics by utilizing the porous silica having interconnected pores. The present invention is based on such knowledge.
By adding the porous silica to the base material, the following actions have been recognized:
(1) Because the lubricant can be supplied to a slide interface continuously, it is possible to allow excellent friction and wear characteristics to continue.
(2) The oil absorption capacity in the composition can be increased by adding the lubricant to resin or elastomer in a range in which moldability of the composition can be secured and adding the lubricant-impregnated porous silica to the base material. Thus the addition amount of the lubricant to the resin or the elastomer is larger than the conventional addition amount of the lubricant.
(3) Because the porous silica impregnated with the lubricant is added to the base material, the lubricant component is held by the porous silica. Therefore, compared with the method of adding a large amount of the lubricant to the resinous material, the following disadvantages do not occur: a screw slips in injection molding, metering is unstable, which makes a cycle time long, dimensional accuracy is unstable, the lubricant attaches to the surface of a die, which causes the surface of a molded product to have poor finish.
(4) It is possible to accomplish kneading of combinations of materials that has not been hitherto made, because of poor compatibility between the lubricating oil and the resin as well as the elastomer.
(5) Because the spherical porous silica, especially true spherical silica, is destroyed by a shearing force of a slide interface, it does not injure even a soft slide mating material.
(6) If the lubricant and the reinforcing material are added separately to the base material in using oil-containing resin and a reinforcing material, the lubricant is locally present on the interface between the reinforcing material and the resin. Thus there is a possibility that reinforcing effect cannot be obtained. However, if the lubricant and the reinforcing material are kneaded, with the spherical porous silica impregnated with the lubricant, the lubricant is not present on the interface between the reinforcing material and the resin. Thus the reinforcing effect can be obtained.
The slide product of the present invention is formed from the composition having lubricity. The slide product is a slide bearing and a retainer for holding a rolling element of the rolling bearing. Further the slide product is a seismically isolated apparatus having a slide support disposed between a lower body thereof and an upper body thereof.
In the slide bearing or the retainer for the rolling bearing, the oil-holding porous silica holds most of the lubricant. Thus the lubricant disperses uniformly inside the porous silica. The lubricant held by the porous silica oozes at a uniform speed for a long time on the contact portion between the retainer and the rolling element disposed on the slide surface of the slide bearing or on the surface of the retainer. That is, the lubricant displays preferable lubricating characteristic.
In the case where a lubricating oil-guiding fibrous filler is used in combination with other components, the lubricant contained in the spherical porous silica present inside passes the surface of oil-guiding fiber, namely, on the interface between the synthetic resin and the fiber and oozes to the surface of the retainer at a stable speed for a long time. Thus the lubricant displays preferable lubricating characteristic.
The rolling bearing incorporating the retainer composed of a molded material of the resinous composition has a small rotational torque and little fluctuation in torque. Further the rolling bearing is lubricated favorably for a long time, it is very durable.
The seismically isolated apparatus of the present invention is obtained as a result of research for reducing the coefficient of friction of the slide surface supposing that a big seism has occurred and for reducing the dependency of the coefficient of friction on speed. By using a molded product of a resinous composition containing the lubricant-impregnated porous silica as at least one of slide surfaces, it is possible to obtain the seismically isolated apparatus has a sufficient degree of strength and wear resistance and a low coefficient of friction having a low degree of dependency on speed is obtained owing to the lubrication.